Watersipora subatra

Science images: Do these strange “moss animals” threaten the ecological balance of the oceans?

Originally from Japan, Watersipora subatra is gradually invading the oceans and seas of the globe. The introduction of a species into a new ecosystem can sometimes lead to irremediable ecological imbalances. In the marine environment, their consequences can be serious due to the difficulty of intervention.

There are some spectacular examples, such as the tropical green algae Caulerpa taxifolia in the Mediterranean or the king crab in Kamchatka. These crabs, originating from the Bering Sea between eastern Russia and Alaska, were introduced into the Barents Sea to develop a fishery there and support local employment. Finding favorable ecosystems, this species quickly extended its range westward and colonized the coasts of Norway, currently as far as the Lofoten Islands. It represents a threat to the ecosystems it colonizes and whose functioning it profoundly disrupts, in particular by ingesting fish eggs, in particular those of pout and cod.

Fortunately, in the majority of cases, introduced species are more discreet, which does not exclude monitoring them in order to detect any disturbance in the functioning within ecosystems or the disappearance of other species.

The bryozoan Watersipora subatra illustrates the example of a discreet introduction but a very effective ability to colonize new environments – originating in Japan, it has spread widely throughout the Brittany coast in just a decade.

If its arrival in Europe may be due to the presence of colonies in the spat (juveniles) of Japanese oysters, its expansion could also take place via the attachment of its larvae or colonies to the hulls of ships (a phenomenon commonly called ” fouling”), or by drifting algae on which colonies could develop.

A variety of “foam animals” around the world

Bryozoans, literally “moss animals”, are colonial animals, mostly fixed on a substrate, inert or alive, and mostly marine. Each individual, called a zoid or zoecia, lives in a millimetric chamber within a colony, the zoarium, which can be encrusting, erect or shrubby and measure from a few centimeters to several tens of centimeters. The nutrition and respiration of bryozoans are ensured by a current of water created by a crown of tentacles called “lophophore”. Since the lodges are most often carbonated, several species thus contribute in warm seas to the construction of coral reefs. The shape, size and arrangement of the chambers make it possible to recognize the different species.

By their larvae or their colonies present in the “fouling”, some species are easily transported from port to port and are currently colonizing the European coast.

Such is the case of Watersipora subatra, native to Japan, which is currently recorded as an introduced species in the North-East Atlantic, the Indo-Pacific (Indonesia), the South-West Pacific (Australia, New Zealand) and the Northeast Pacific (California). The taxonomy of this genus, which includes 13 species that are sometimes very similar morphologically, led to many hesitations before the definitive identification of the Watersipora present on the European coasts was fixed.

Along the European Atlantic coasts, this species was initially identified as Watersipora aterrima in the Arcachon basin between 1968 and 1973, then as Watersipora subovoidea in Brittany in 2005, revised as Watersipora subtorquata in 2009. It is now known that the species present in Brittany, around the British Isles and in the North Sea is in fact Watersipora subatra and that four other species are present on the rest of the European coasts.